State changes propagate virally through peers storing any given contract. If a peer doesn't get an update for whatever reason there are a variety of mechanisms that get it back in sync ASAP, so it will be eventually consistent.

The contract ensures that the state is valid both before and after any change and every peer who sees the state will ensure it is valid, so it is verifiable computation in that sense.

Happy to chat - you can pm me on reddit or twitter, username "sanity" in both cases.